Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 1: Superconductivity - Fabrication and Characterization

TT 1.1: Vortrag

Montag, 26. März 2007, 09:30–09:45, H18

Critical state in current-carrying NbN thin-film structures — •Konstantin Ilin¹, Michael Siegel¹, Andreas Engel², Holger Bartolf², Andreas Schilling², Eugen Hollmann³, Alexei Semenov⁴, Andrey Smirnov⁴, and Heinz-Wilhelm Hübers⁴ — ¹Institute of Micro- and Nano-Electronic Systems, University of Karlsruhe, Germany — ²Physics Institute, University of Zurich, Switzerland — ³Research Centre Jülich, Germany — ⁴DLR Institute of Planetary Research, Berlin, Germany

Superconducting NbN thin films are widely used for fabrication of detectors of electromagnetic radiation: single-photon detectors (SPD) and hot-electron mixers (HEM). While SPD is a meander line of width smaller than 100 nm, the key part of HEM is a few micrometers wide bridge with length of 200 - 300 nm. We report on a study of current-generated critical states in NbN bridges made from ultra-thin (< 10 nm) films. The films were deposited by reactive magnetron sputtering onto heated Si and sapphire substrates and patterned by electron-beam lithography and ion-milling to form bridges of width from 100 nm up to 10 μm. The critical current value of all bridges was measured in the temperature range from 2 K up to Tc. We observed significant variations of Ic(T) curves with the bridge widths. Sub-micrometer wide structures demonstrate almost standard dependencies of Ic on temperature, which can be described by the Ginzburg-Landau theory. Bridges of several micrometers in width show strongly non-monotonic Ic(T) dependencies. Mechanisms determining the current-carrying ability of the bridges made from ultra-thin NbN films will be discussed.